The present invention relates to process instruments such as pressure transmitters which have end caps that are threaded for removal and more particularly to locking mechanisms for such end caps.
2. Description of the Prior Art
Process instrumentation such as pressure transmitters are known wherein the end covers of the transmitter have outwardly projecting flanges having a bolt hole therein. The end cover is screwed on to the transmitter until tight and the bolt hole is aligned with a threaded bolt hole in the transmitter housing itself. A bolt is then passed through the flange and the bolt hole with the bolt threaded in to thereby lock the flange to the transmitter housing and thus lock the end cover to the same housing preventing the unthreading of the cover until the bolt is removed freeing the flange from the transmitter housing.
Although this type of cover lock prevents the accidental unscrewing of the end caps, the bolt, when removed, is sometimes lost and the cover lock's purpose is thereby defeated. Similarly, the flange is difficult to align with the bolt hole in the housing causing either a loose fit between the housing and the end cap or in some cases an overturning of the end cap which may cause the threads on the housing to be stripped in an attempt to align the flange with the bolt hole. Note that the aluminum die casting alloy typically used in this industry for transmitter housings and end caps is indeed sensitive to stripping and galling due to overtorqueing.
Other transmitter cover locks are known wherein each cover of the transmitter has a flange which is captured by a flat middle piece and is then screwed to the housing.
Again, there is the problem of alignment of the cover lock with the locking piece as well as the possibility of losing the locking piece whenever the assembly is unscrewed.